1. Field of the Invention
The present invention relates to a seat and more specifically to a seat such as a vehicle seat loaded on a vehicle.
2. Description of the Related Art
Conventionally, the vehicle seat loaded on a vehicle such as automobile has been modified in various ways in order to protect passengers when a collision occurs (see, for example, Japanese Patent Application Laid-Open (JP-A) No. H6-1174 and JP-A No. H11-115594).
JP-A No. H6-1174 has described a vehicle safety seat in which reinforcement members are provided in the vehicle widthwise direction at the proximal end on the side of seat cushion in a seat back, in consideration of a collision from sideway of a vehicle. According to this vehicle safety seat, when a collision occurs from sideway of a vehicle, the reinforcement members transmit an impact load received from a side of the vehicle to a side end portion on an opposite side thereof, preventing a seat from being deformed to secure a space for a passenger.
JP-A No. H9-272368 has described a vehicle seat in which the cushion (back rest) of a seat back or the seat back itself can be moved backward substantially in parallel with the seat cushion, that is, a vehicle body. According to this vehicle seat, when a collision occurs from backward of a vehicle, the cushion of a seat back or the seat back itself is moved backward substantially in parallel while its impact absorbing material is being deformed, so as to absorb an impact in conditions in which a passenger is supported securely on the seat back.
JP-A No. H11-278128 has disclosed a vehicle seat in which a cross member in which an inner pipe is inserted slidably is provided in a stretched manner over a pair of right and left outer pairs, cantilevered by each of right and left side frames at a bottom between right and left side frames which constitutes a seat back frame.
In this vehicle seat, if a seat occupant is pressed against the seat back at the time of a collision from backward, the cross member deflects backward significantly while maintaining a state in which each outer pipe is connected to the inner pipe, so as to absorb an impact at a large stroke. For the reason, the stiffness of the side frame does not need to be reduced to guarantee the displacement of the cross member backward and therefore, the stiffness of the seat back frame can be secured.
JP-A No. H11-32865 has disclosed a seat back frame structure in which a connecting member which is formed in a shape of inverted letter U open downward for connecting right and left vertical frames on the seat back frame is provided and a connecting portion in the connecting member to the vertical frame is formed in a flat portion which deforms by a collision load.
With this structure, when a collision load is inputted to the seat back frame at the time of a collision, the flat portion of the connecting member deforms to reduce the impact load acting on a seat occupant and at the same time, preventing generation of a bending destruction in the vertical frame.
JP-A No. H11-115594 has disclosed a vehicle seat in which a brittle portion is provided in the middle portion in the front-rear direction of a lower arm to whose rear end a seat back is connected and when a vehicle collision occurs, the brittle portion of the lower arm deforms to tilt the seat back backward. That is, with this structure, the seat back entirely tilts backward when the vehicle collision occurs.
Further, for example, JP-A No. 2000-185582 and JP-A No. 2003-25891 have disclosed a seat in which upon a collision, the head rest automatically moves relative to the seat back in order to suppress the moving of the head portion of a seat occupant, thereby reducing disasters of whiplash of the passenger.
JP-A No. 2000-185582 has disclosed an automobile seat in which a head rest mounting portion is provided on the top end portion of an impact receiving frame fixed on the top side pipe of a seat back frame. According to this automobile seat, when a seat occupant is pressed against the seat back upon a collision, a portion under the top side pipe of the impact receiving frame moves backward while the top side pipe is twisted and then, the head rest mounting portion is directed forward, so that the head rest automatically moves to the side of the head portion (forward) of the seat occupant.
JP-A No. 2000-325179 has disclosed a vehicle seat structure in which a head rest moving frame disposed within the seat back is supported by the seat back frame through a link mechanism. According to this vehicle seat structure, when the waist portion of a seat occupant presses a strap member stretched on the bottom of the head rest moving frame backward, this pressing direction is converted by the link mechanism so that the head rest moves upward and forward linearly.
Adopting this link mechanism has realized such a structure in which the head rest is moved only by a necessary amount by receiving a load from the waist portion whose timing of applying a load of the seat occupant on the seat back is earlier than the breast portion.
JP-A No. 2003-25891 has described a vehicle seat in which paired right and left side frames, which constitute the seat back frame, comprise: “side frame uppers” (side frame upper portions) whose top ends are each supported movably in the vertical direction relative to a vehicle body while a head rest is fixed thereon; and “side frame lowers” (side frame lower portions) whose bottom ends are supported rotatably relative to the vehicle body, and the side frame upper and the side frame lower are connected rotatably to the vehicle body at the front side of a virtual straight line which connects up and down supporting points.
Further, cloth member having cushion characteristic is provided in a stretched manner over this seat back frame.
According to this vehicle seat, when the seat occupant presses the cloth member backward upon a collision from backward, the side frame upper and side frame lower rotate relative to each other in a direction for increasing an angle formed between the both, moving the head rest upward and forward.
However, in the composition described in the above JP-A No. H6-1174, only securing a space for a passenger at the time of a collision is considered and a collision from backward is not considered. Further, according to the structure described in JP-A No. H9-272368, because the seat back cushion or seat back itself is moved backward substantially in parallel, there is a fear that the moving stroke is likely to be limited and if the stroke is small, the impact energy cannot be absorbed sufficiently (a load acting on the passenger increases in energy absorption process).
Further, according to the structure disclosed in JP-A No. H11-278128, because the stiffness of the seat back frame is high and the impact energy is absorbed by only deformation of the cross member, there is a fear that the load acting on the seat occupant may not be dissipated in the energy absorption process and concentrated on the waist portion of the passenger. The configuration disclosed in JP-A No. H11-32865 can generate the same problem.
Because there is a tendency that the head portion of the passenger tilts backward (moves) with a delay from the upper body, unless a sufficient energy is absorbed from the passenger at the initial period of the collision, the remaining energy tending to move the head portion backward increases, so that protecting the head portion sufficiently becomes difficult. Thus, to protect the head portion sufficiently at the time of a collision from backward, the energy of the upper body needs to be absorbed sufficiently in the seat back and thus, the seat needs to follow up changes in posture (load) of the passenger with a passage of time and dissipate the load acting on the passenger. However, this point has not been considered in JP-A No. 2000-185582 to JP-A No. 2003-25891.
More specifically, in the respective configurations of JP-A No. 2000-185582 and JP-A No. 2000-325179, the seat back frame formed in the shape of inverted letter U, which is open downward and whose bottom end portion is connected with a reinforcement member or a lower frame has a high stiffness and its impact absorbing frame or head rest moving frame which permits only a displacement due to twisting of the top side piep or pulling of the tension spring does not provide a sufficient impact absorption stroke and thus, the impact energy of a seat occupant cannot be absorbed sufficiently prior to restriction of the moving of the head portion by the head rest.
Further, according to the configuration of JP-A No. 2003-25891, because the backward moving of the top end of the side frame upper is restricted although the seat back frame is constituted of the side frame upper and side frame lower, which are connected to each other rotatably, the impact energy trying to move the passenger backward cannot be absorbed sufficiently. Further, because this configuration supports the top end of the side frame upper relative to a vehicle body, this cannot be applied to for example, front seats of the vehicle.